The Reseach Of Phytoplankton Community Of The Donghu Lake And Taxonomic Studies On Diatom

The phytoplankton community structure and its seasonal succession of the Donghu Lake(Guozheng Hu)were studied during 2013.12 to 2014.11.Combining with the physical and chemical indicators,the relationship between planktonic diatom community structures and the environmental factors were analyzed,the nutritional status of the Donghu Lake was evaluated.Meanwhile,We proformed the study on the morphology and molecular phylogeny in three diatoms which were isolated and purified in the Donghu Lake,Modao Stream and Xiaoyue Lake.During the experiment period,the 165 species belonging to 8 phyl?m and 61 genera were identified.Among them 72 species of 21 genera belonging to Bacillariophyta,23 species of 11 genera to Cyanophyta,51 species of 17 genera to Chlorophyta,4 species of 2 genera to Cryptophyta,7 species of 4 genera to Englenophyta,2 species of 1genera to Pyrrophyta,3 species of 3 genera to Chrysophyta and 3 species of 2 genera to Xanthophyta.The phytoplankton was mainly composed of Bacillariophyta,Cyanophyta,Chlorophyta and Cryptophyta,the species composition of Bacillariophyta and Chlorophyta was the most abundance.The species composition of phytoplankton was obviously different among four sites,butthe biomass was not different significantly.As Cyanobacterial blooms,the cell density of phytoplankton in s?mmer and aut?mn(2.49-15.9×107cell/L)was apparently higher than that of in spring and winter(0.09-6.0×107cell/L).The phytoplankton community had an obvious seasonal succession,the succession pattern of the phytoplankton as this:Bacillariophyta,Cryptophyta(Spring)?Cyanophyta,Chlorophyta(S?mmer)?Bacillariophyta,Cyanophyta(Aut?mn)?Cryptophyta(Winter)in the Donghu Lake.Comparing the physicochemical indices and phytoplankton characteristics in four sites showed that the water quality in central region was better than that of the littoral zone.As one of the main phytoplankton groups of the planktonic diatoms accounts for about 44% of the total species,and contributed 16% biomass to the phytoplankton of the Donghu Lake.Altho?gh the species of pennate diatom was rich,the centric diatom was predominant by quantity.The dominant diatom species were Cyclotella meneghiniana,Aulacoseira distans and Melosira granulate.Compared with the results of the study in 1994,the species of planktonic diatom were significantly reduced.The biomass of planktonic diatoms showed an obvious seasonal change,the cell density in spring and aut?mn were higher than that of in winter and s?mmer.The diversity index of plankton diatom revealed that the water was moderately polluted in the Donghu Lake and the water quality in central region was better than that of the littoral zone.The redundancy analysis(RDA)between planktonic diatom community and environmental factors indicated that the planktonic diatom community structure was correlated significantly with TP and TDP.Based on the determination of three diatom gene sequence(SSU nrDNA and ITS nr DNA),the phylogenetic tree was constructed and the analysis of genetic differences was done at the molecular level.Meanwhile,combined with morphological characteristics,thethree diatoms were identified.The result showed that MD1 and DH1 were Cyclotella meneghiniana and Stephanodiscus hantzschii.The morphological characteristics of XYH1 were similar with Achnanthidium catenatum,but the sequence was homology close with Achnanthidium saprophilum.It may be a subspecies of Achnanthidium saprophilum.